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281.
Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest 总被引:1,自引:1,他引:0
Gabriel Katul Cheng-I Hsieh David Bowling Kenneth Clark Narasinha Shurpali Andrew Turnipseed John Albertson Kevin Tu Dave Hollinger Bob Evans Brian Offerle Dean Anderson David Ellsworth Chris Vogel Ram Oren 《Boundary-Layer Meteorology》1999,93(1):1-28
The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (u, w) and temperature (T) are more planar homogeneous than their vertical flux of momentum (u*
2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed. 相似文献
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中国大部分狗头金分布在湖南、四川、黑龙江、青海与山东五省。狗头金分布与水系有密切关系。狗头金可划分为两大类成因类型:表生成矿型(物理风化、化学溶解、再生-齐汞化)与原生成矿型(原生金块与原生改造)。含金地貌与新构造运动在成矿作用中占有重要地位。 相似文献
284.
基于533年旱涝指数场序列,采用了滑动累积频率法用于降水序列重建工作,并选用了3种不同均值用于序列重建试验,得到了1499~2002年共504年连续的滑动平均降水场序列。分析表明,重建的504年降水场序列与49年实测降水场序列相关性较好,其平均相对均方误差在1.89%以下;重建的序列与原旱涝指数序列的非线性关系,表明重建序列是合理的,为华北地区长期旱涝变化规律的研究提供了基础资料。 相似文献
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287.
华能南京电厂不同粒径粉煤灰中微量元素分布及其富集规律 总被引:8,自引:3,他引:8
华能南京电厂不同粒径粉煤灰的化学成分和矿物相组成基本相同,煤粉所含矿物质在高温燃烧过程中的挥发-凝聚作用,导致微量元素趋向细粒径粒煤灰中富集,其富集的程度则与粉煤灰的平均粒径和元素的地球化学性质密切相关,粉煤灰排放的环境效应表明,尤以细粒径灰粒的影响最大。 相似文献
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289.
区域重力调查是一项基础地球物理调查工作。它的成果可用于研究地质构造、资源勘探、环境调查,地震灾害、地球形状、地球物理理论等方面。它象征着一个国家科学技术发展水平,特别是地学方面的水平。地矿部研究了国内外重力勘查情况,于1978年提出并组织、实施了全国范围的区域重力调查。通过十多年的工作,取得了丰硕成果。本文就地矿部区域重力调查成果与展望,予以论述。 相似文献
290.
The characteristic structures of the Precambrian cherts from the Gusui section, Guangdong ,Chi-na, include bedded structure ,laminated structure ,massive structure and pseudobrecciated structure.The chert is characterized by consistently low abundance of TiO2,Al2O3 and most trace elements.Howevver ,it is enriched in Ba,As,Sb,Hg and Se.In Al-Fe-Mn ternary diagrams,it falls into the “hydrothermal field“ .Correspondence analysis and factor analysis show that many elements show up in the factor that represents the leaching of country rocks by hydrothermal solutions,and are the very characteristic element association fo the geochemically anomalous South China basement.Petrologic and geochemical evidence suggests a hydrothermal origin for the chert.The chert may have been formed in a Precambrian fift or an extension zone developed within the Yunkai marginal geosyncline, with a fault system linking it to an unknown heat source at depth. 相似文献